cpufreq: use last policy after online for drivers with ->setpolicy

For cpufreq drivers which use setpolicy interface, after offline->online
the policy is set to default. This can be reproduced by setting the
default policy of intel_pstate or longrun to ondemand and then change to
"performance". After offline and online, the setpolicy will be called with
the policy=ondemand.

For drivers using governors this condition is handled by storing
last_governor, during offline and restoring during online. The same should
be done for drivers using setpolicy interface. Storing last_policy during
offline and restoring during online.
Signed-off-by: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

drivers/cpufreq/cpufreq.c

@@ -976,10 +976,14 @@ static int cpufreq_init_policy(struct cpufreq_policy *policy)
 
 	new_policy.governor = gov;
 
-	/* Use the default policy if its valid. */
-	if (cpufreq_driver->setpolicy)
-		cpufreq_parse_governor(gov->name, &new_policy.policy, NULL);
-
+	/* Use the default policy if there is no last_policy. */
+	if (cpufreq_driver->setpolicy) {
+		if (policy->last_policy)
+			new_policy.policy = policy->last_policy;
+		else
+			cpufreq_parse_governor(gov->name, &new_policy.policy,
+					       NULL);
+	}
 	/* set default policy */
 	return cpufreq_set_policy(policy, &new_policy);
 }
@@ -1330,6 +1334,8 @@ static void cpufreq_offline_prepare(unsigned int cpu)
 		if (has_target())
 			strncpy(policy->last_governor, policy->governor->name,
 				CPUFREQ_NAME_LEN);
+		else
+			policy->last_policy = policy->policy;
 	} else if (cpu == policy->cpu) {
 		/* Nominate new CPU */
 		policy->cpu = cpumask_any(policy->cpus);

include/linux/cpufreq.h

@@ -77,6 +77,7 @@ struct cpufreq_policy {
 	unsigned int		suspend_freq; /* freq to set during suspend */
 
 	unsigned int		policy; /* see above */
+	unsigned int		last_policy; /* policy before unplug */
 	struct cpufreq_governor	*governor; /* see below */
 	void			*governor_data;
 	bool			governor_enabled; /* governor start/stop flag */